JPH1150122A - Dephosphorize-refining of molten iron in converter type refining vessel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent slag foaming at the time of completing oxygen blowing and to execute smooth dephosphorize-refining of molten iron in a high productivity, in the dephosphorize-refining of the molten iron in a converter type refining vessel. SOLUTION: (a) Molten iron is charged into the converter type refining vessel and (b) the basicity (CaO/SiO2 ) of the slag at the time of completing the oxygen-blowing the molten iron, is regulated to 2.2-4.0 and carbonaceous material before and after completing the oxygen-blowing, is charged by >=1 kg/ton of molten iron into the converter type refining vessel. (c) Inert gas is blown by >=0.08 Nm<3> /ton/min from the furnace bottom of the converter type refining vessel for at least 2 min from the time of charging the carbonaceous material. At the time of charging the carbonaceous material, this material is dividedly charged for 1-3 min. Further, the charge of iron ore is desirable to be completed at least 5 min before the time of completing the dephosphorize- refining.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to dephosphorization and refining of hot metal in a converter type refining vessel, and more particularly to performing smooth and highly productive dephosphorization of hot metal by preventing slag forming at the end of blowing. About the method.

[0002]

2. Description of the Related Art In a conventional converter steelmaking method, hot metal dephosphorization and decarburization refining are performed in the same converter to complete the steelmaking operation. However, while the demand for steel quality in recent years has increased, with the expansion of continuous casting, vacuum degassing, and secondary refining of molten steel such as ladle refining, the tapping temperature in converters has increased, The dephosphorization capacity in the converter has been reduced. The reason for this is that the dephosphorization reaction proceeds disadvantageously as the temperature increases.

[0003] Therefore, a hot metal pretreatment method has been developed in which the hot metal charged into the converter is preliminarily treated, and in particular, the phosphorus (P) component is removed to some extent before the hot metal is charged into the converter. As one of the methods, in a converter type refining vessel (hereinafter referred to as a converter, etc.), refining for dephosphorizing and decarburizing hot metal in the same converter or the like is stopped, and one converter For example, there has been proposed a steelmaking method in which hot metal is dephosphorized and the dephosphorized hot metal is transferred to another converter or the like for decarburization refining.

[0004] As such a technique, Japanese Patent Laid-Open No. 2-20071 is disclosed.
No. 5, Japanese Patent Publication No. 2-14404, Japanese Patent Publication No. 61-
There is a proposal in JP 23243 Gazette. In addition, the inventor of the present application has also remodeled a conventional steelmaking plant, provided working floor openings in the working floor in front of each of a plurality of converters, and received molten metal obtained by dephosphorizing hot metal in one converter. A refining method has been developed in which a hot pot is received, and the hot pot is transported to another converter through the opening of the work floor, charged into the converter, and decarburized and refined therein (Japanese Patent Laid-Open No. Hei 6 (1994)). -41624).

[0005]

In the above steel making method, it is necessary to perform dephosphorization and refining of hot metal in one converter and immediately discharge the hot metal and decarburize and refine the hot metal in another converter and the like for smooth steel making. is necessary. However, the dephosphorization and refining of the hot metal is performed at a low temperature (1250 to 1400 ° C.), and the slag is formed because the slag has a high FeO (15 to 20%) for the dephosphorization of the hot metal. If the hot water is discharged immediately, slag flows out of the furnace port, or a large amount of slag flows into the hot pot, and overflows from the hot pot to cause various problems.

Therefore, after oxygen blowing, rinsing is carried out until slag forming subsides, for example, usually 6 to 10 hours.
You have to wait for a bath for a minute. Therefore, there is a problem that the efficiency of the entire steelmaking operation is reduced. Therefore, in the present invention, a method for dephosphorizing and refining hot metal in which rinsing is performed for about 2 minutes after the completion of the dephosphorizing and refining of the hot metal, and then slag forming is calmed down within 5 minutes. As an issue.

[0007]

As a result of various studies on the above problems, the following inventions have been made. A first invention is a method for dephosphorizing and refining hot metal in a converter type refining vessel comprising the following steps. (A) Hot metal is charged into a converter type refining vessel, and (b) the basicity of slag (CaO /
SiO ₂ ) is set to 2.2 to 4.0, and 1 kg / ton of carbon material is placed in a converter type refining vessel before and after the end of oxygen blowing.
(Hot metal) or more, and (c) at least 2 minutes or more from the bottom of the converter type refining vessel from the time of charging the carbon material.
Inert gas of 08 Nm ³ / ton / min or more is blown.

In a second aspect, the carbon material is added at a rate of 1 kg / to.
This is a method for dephosphorizing and refining hot metal in a converter type refining vessel, wherein when charging n (hot metal) or more, it is divided and charged separately for 1 minute to 3 minutes.

In a third aspect of the present invention, in the dephosphorizing and refining of the hot metal, charging of the iron ore is completed at least 5 minutes before the end of the oxygen blowing, and the hot metal is supplied to the converter type refining vessel. Dephosphorization refining method.

[0010]

FIG. 8 conceptually shows the state of dephosphorization and refining of hot metal 4 in a converter type refining vessel 2 of 340 ton of hot metal. After charging the hot metal, oxygen is blown from the lance 12, and a predetermined amount of calcined lime or the like is charged to generate slag 6 mainly composed of CaO, SiO ₂ , FeO, etc., and remove phosphorus from the hot metal. In this case, the converter type refining vessel freeboard (hot metal from the melt surface to throat height, H _F) is also 7.5 m,
The slag 6 forms and reaches near the furnace opening 10.

When the dephosphorization and refining of the hot metal is completed, the furnace is turned down and the molten metal is discharged to the ladle through the tapping hole 8. At this time, if the slag is formed at a high level, the slag overflows from the furnace opening or the hot pot and contaminates the lower part of the furnace. Therefore, it is necessary that slag forming be as calm as possible before tapping.

FIG. 6 shows an outline of the dephosphorization refining of hot metal. After charging 340 ton of hot metal, calcined lime (3 to 6 ton / c
h), oxygen blowing is performed for about 12 minutes while charging fluorite (0.6 ton / ch) and the like. Conventionally, after that, rinsing is performed for about 2 minutes to separate hot metal and slag. After that, in order to calm down slag forming, 6-
Wait 10 minutes (average 8 minutes) before tapping. The tapping time (from the start of the falling furnace to the end of tapping) usually takes about 5 minutes.

That is, an average of 8 minutes was required from the start of rinsing to the start of hot water supply (hereinafter, this time is referred to as a soothing time).
FIG. 6 shows an embodiment of the present invention, and the sedation time is 4 minutes. In the present invention, the above-mentioned calming time is set within 4 minutes on average, and the entire steel making time is shortened by at most 4 minutes, thereby improving the steel making efficiency. Here, whether or not the slag forming was calmed was based on whether or not the slag height in the furnace was 1 m or less.

First, FIG. 1 shows the relationship between the basicity of slag and the calming time of slag when coke is not charged as a carbon material. From FIG. 1, when coke powder (having a diameter of 10 mm or less) is not charged into the slag as a carbon material, if the basicity (CaO / SiO ₂ ) is about 2.2 or more, the soothing time is about 10 minutes or less. Become.

It is considered that the reason for this is that if the basicity of the slag is 2.2 or more, the silicate ions in the chain of slag are fragmented, and the viscosity of the slag decreases.
On the other hand, when the basicity is 4 or more, the melting point of the slag is 1400.
° C or higher, the slag does not melt at the dephosphorization refining temperature (1400 ° C or lower), and the slag forming is small,
This is not desirable because dephosphorization refining does not proceed.

Next, the basicity of the slag is about 2.2 to 2.6.
In the case of, the relationship between the charging amount of coke powder to be charged at the end of oxygen blowing and the slag calming time was examined, and is shown in FIG. It is clear that when the charging amount of coke powder is 1 kg / ton (hot metal) or more, the calming time is 5 minutes or less.

Although there are various theories as to why coke powder calms slag forming, there are various theories.
It is estimated that outgassing by O gas is improved. Examples of the carbon material include coke powder (having a diameter of 10 mm or less), carbonate, and petroleum coke.

As described above, at the end of the dephosphorization refining of hot metal, when the slag basicity is set to 2.2 or more and the coke powder is charged at 1 kg / ton (hot metal) or more, the slag forming is performed within 5 minutes. Because it calms down, safe tapping is possible. In addition, the charging method of the carbon material such as coke powder and the like may be all at once, but desirably, for example, the charging amount at one time is 0.2 to 0.3 kg / ton and the amount is 1 to 4 kg. It is advisable to charge them separately over a period of minutes.

The reason is that the carbon material reacts with FeO of the slag to generate CO gas and temporarily activates the slag forming, so that it is more desirable to charge the carbon material separately than to charge the entire amount at once. Further, the charging time of the coke powder is preferably started after the end of the oxygen blowing, and the first half of the rinse start time is desirable.

Next, the relationship between the slag forming calming time and the rinsing time is shown in FIGS. In the figure, the basicity is 2.0 to 3.5, and the carbon material is 1.5 to 2.
5 kg / ton is charged. Figure 3 shows a case bottom-blown gas amount of 0.05~0.07Nm ³ / ton / min, Fig. 4 is a bottom-blown gas amount 0.08～0.10Nm ³ /
This is the case of ton / min. From these figures, when the bottom blowing gas amount is 0.08 Nm ³ / ton / min or more, rinsing for 2 minutes results in a calming time of about 4 minutes or less.

In ordinary dephosphorization refining, P in hot metal reacts with FeO in slag and is absorbed by the slag.
Therefore, in order to promote dephosphorization refining, FeO in slag
Increase the concentration. For this purpose, iron ore or mill scale is charged or charged in the middle stage of blowing.

However, if the slag has high FeO, the slag forming becomes large after the end of oxygen blowing. Therefore, the relationship between the elapsed time after charging the iron ore and the slag calming time was examined. The result is shown in FIG. As shown in FIG. 5, it is clear that the slag has been calmed down by the ore charging when 5 minutes or more have passed after the iron ore charging. Therefore, in the present invention, the iron ore charging is performed as if the iron ore had ended 5 minutes or less before the oxygen blowing end time.

Here, the converter type refining vessel refers to an upper-bottom blow converter, a bottom blow converter and the like. The present invention can be implemented in any of these converters. The inert gas may be an Ar gas, a nitrogen gas in some cases, or a mixed gas thereof. Furthermore, the method of injecting gas from the converter furnace bottom may be a method using a nozzle, a porous brick, or the like disposed on the furnace bottom.

[0024]

Embodiments of the present invention will be described below. The test was performed for three months to confirm the effect of the dephosphorization refining method according to the present invention. In each month, 16 to 30 charges per day (c
h), the test was carried out for a minimum of 22 days in each month, and the average value per month was calculated for the component composition and the like, and the operation results are shown in Table 1 in FIG. In addition, specific technical contents of dephosphorization and refining of hot metal (
The lance height, the amount of bottom blown nitrogen, the amount of slag forming material such as calcined lime and fluorite, and the timing thereof are as shown in FIG. 6 described above.

As shown in Table 1 of FIG. 7, the P of the hot metal before the dephosphorizing refining is about 0.1 wt%, but after the dephosphorizing refining, it is dephosphorized to about 0.03 wt%. Has been achieved. The time for calming the slag is about 4 minutes as shown in FIG. On the other hand, conventionally, this time is a maximum of 10 minutes and an average of 8 minutes, and the steel making time is reduced by 4 minutes.

[0026]

By performing the dephosphorization and refining of the hot metal according to the present invention, the time for the dephosphorization and refining of the hot metal can be reduced on average by about 4 minutes. So-called steelmaking time is 3 per charge
Since it is 0 minutes, the steel making time can be reduced by about 13%. This means a 13% increase in productivity. This effect is extremely large, the improvement in production efficiency is enormous, and the industrial effect is remarkable.

[Brief description of the drawings]

FIG. 1 shows the relationship between slag basicity and slag sedation time.

FIG. 2 shows the relationship between the amount of coke powder charged and the slag calming time.

FIG. 3 is a diagram showing an example of a relationship between a rinsing time and a sedation time.

FIG. 4 is a diagram showing another example of the relationship between the rinsing time and the sedation time.

FIG. 5 is a diagram showing the relationship between the time after charging the iron ore and the slag calming time.

FIG. 6 is a diagram illustrating a dephosphorization refining process of hot metal in the present invention.

FIG. 7 is a view showing an embodiment of the dephosphorization refining of hot metal in the present invention.

FIG. 8 is a conceptual diagram of dephosphorization refining of hot metal in a converter type refining vessel.

[Explanation of symbols]

 2 Converter type refining vessel 4 Hot metal 6 Slag 8 Tapping port 10 Furnace port 12 Lance

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tomoo Izawa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (3)

[Claims] 1. A method for dephosphorizing hot metal in a converter type refining vessel, comprising the following steps: (A) Hot metal is charged into a converter type refining vessel, and (b) the basicity of slag (CaO /
(SiO ₂ ) is set to 2.2 to 4.0, and before and after the end of oxygen blowing, 1 kg / ton (hot metal) or more of carbon material is charged into the converter type refining vessel, and (c) charging of the carbon material An inert gas of 0.08 Nm ³ / ton / min or more is blown from the furnace bottom of the converter type refining vessel for at least 2 minutes from the time. 2. The converter type refining according to claim 1, wherein when charging the carbon material at a rate of 1 kg / ton (hot metal) or more, the carbon material is divided and divided and charged over 1 minute to 3 minutes. A method for dephosphorizing and refining hot metal in a vessel. 3. The converter type refining according to claim 1, wherein in the dephosphorization of the hot metal, the charging of the iron ore is completed at least 5 minutes before the end of the oxygen blowing. A method for dephosphorizing and refining hot metal in a vessel.